The present invention relates generally to the storage of information on data storage mediums. More particularly, the invention relates to variable bit density recording in data storage mediums.
Disc drives have utilized circular tracks for recording information on discs having a magnetic coating on the surface. It is a goal of a disc drive designer to provide as much storage capacity as possible. For a given physical structure, this can be accomplished by increasing the amount of data recorded on a track.
The surfaces of each disc have been divided into recording zones and the frequency of recording within a zone is maintained constant in order to maintain a relatively constant bit density across the recording surface. The recording frequency in each zone differs. The recording bit density in each zone is a function of the ratio of the recording frequency over the linear velocity of the rotating disc drive. Thus, the recording bit density in each zone is the same across each disc.
FIG. 1 illustrates the recording zones in a typical hard drive. There is shown a pair of discs 100 and 102 in a disc drive, each disc having recording zones defined as Z1, Z2, and Z3. The zones in the two-disc drive are vertically aligned and the boundaries of the zones are defined radially by the distances indicated by R1-R4 based on the distance from the center C of the disc. The recording frequency used in each zone of each disc is the same. Thus, the recording frequency used in Zone Z1 of disc 1 is the same as that used in zone Z1 of disc 2. Furthermore, the recording bit density associated with zone Z1 of disc 1 is the same as that used in zone Z1 of disc 2. The zones are numbered such that the recording frequency decreases as the linear velocity decreases as the zone number increases.
The recording frequency used within each of the zones is determined at the design stage based on various factors, including an expected nominal head read/write performance for the heads to be used in the drive. The performance of each head with its respective surface is measured to determine if it met the minimum performance standard threshold. If any of the heads in a disc array failed to reach at least the minimum threshold, the drive was considered unacceptable and was shipped unless the head could be replaced to meet the minimum performance standard.
The replacement of a failed head can become an expensive task. In some cases, a failed head can miss the minimum performance standard threshold by a slight margin. In these cases, the replacement of the failed head is needless and it is more economically feasible to attempt to accommodate for the lost storage capacity.
The present invention pertains to an apparatus and method for recording data in a data storage medium. One such data storage medium is a disc drive having at least two recording disc surfaces such as a disc drive having a number of discs, each of which have at least one recording surface. Each recording surface is associated with a read/write head that records and accesses data from the surface. Each recording surface is partitioned into a number of zones. Each zone is vertically aligned with a same zone on each surface of each disc. The zone boundaries on all surfaces of the disc drive are the same. The recording frequency for each zone on all surfaces can differ for each read/write head in order to compensate for a read/write head that cannot meet the BPI error rate threshold.
In accordance with preferred aspects of the present invention, the present invention comprises an apparatus for recording computer readable information on recording surfaces using heads wherein each recording surface having one associated head for recording data to the recording surface. At least one head operates at an actual recording frequency less than the actual recording frequency of one of the other heads according to a dynamically generated physdisk lookup table comprising information related to the different heads and the different recording frequencies. The apparatus includes a microprocessor for controlling the allocation of data using the dynamically generated physdisk lookup table.
In accordance with other preferred aspects, each head and recording surface relates to a predetermined preferred recording frequency and the average value of the actual recording frequencies for the heads is not less than the predetermined preferred recording frequency. Additionally, the physdisk table is generated following error testing of the heads and comprises information used for converting between logical block addresses and physical block addresses. The variable bit density disk drive is capable generating a number of unique physdisk tables equal to a value related to the number of possible bit densities raised to the power of a value related to the number of heads in the disk drive.
In accordance with other preferred aspects, the present invention relates to a method of recording data on a data storage medium having a plurality of recording surfaces and a plurality of heads, each head associated with a particular recording surface wherein the method comprises the following steps: testing the heads to determine error rate characteristics for each head; determining a recording frequency for each head with respect to a predetermined average frequency and maximum error rate criteria; generating a physdisk lookup table based on the determined recording frequencies for the heads; and using the physdisk lookup table to allocate data sectors on the recording media.
These and various other features as well as advantages which characterize the present invention will be apparent from a reading of the following detailed description and a review of the associated drawings.